Do I have to pay all of my last month's rent?

ApartmentFilter: I am currently leasing an apartment month-to-month (continuation of a twelve-month lease which ended in August 2007) and I told my landlord today that I intend to move out around May 18 of this year. He informed me that I would have to pay for the whole month of May instead of prorating the rent because "that's the way rent's done." Is this true?
posted to Ask Metafilter by pmdboi at 9:46 AM on April 4, 2008 (24 comments)